A40 Part Substitutions

I have just completed a second Pass-A40 and wanted to share the results, if you deem it appropriate. This new version differs from the original in that it's power supply has been improved by the use of bypassed 55,000 UF filter caps, a high current toroid transformer and HEXFRED diode bridges. It is being used to drive a pair of Magneplanar 1.6QRs and a second identical amp is now started so each amp can be bridged to supply about 130 watts to each speaker. While there are fans under the large heatsinks, it turns out that the amp runs cool enough with no forced air, which was a main goal for this design as the fans are too loud even when turning slowly. Pictures: Fig.1: Front of amp showing output devices and heatsink modules Fig.2: Rear of modules with toroid, filter caps and input/output connections Fig.3: Closeup of HEXFRED bridge and circuit board with "star" ground connections nearby. Fig.4: Bypass caps across main filter electrolytics Fig.5: Closeup of heatsink circuit board that connects output transistors, emitter resistors and driver board. The connections near the top are for monitoring the bias. Thank-you Nelson for the articles. The sound from this amp is the best I have ever heard and listening to everything from alternative to classical on equipment that is home-made is a wonderful experience. Nick Sirkin